There is currently substantial interest in reducing the size scale of various mechanical systems, and dramatic recent advances have been achieved in the fabrication of microelectromechanical systems. A review of current trends in microelectromechanical systems can be found in W. Trimmer, (1997) Micromechanics and MEMS: Classic and Seminal Papers to 1990, IEEE Press, New York. Ultimately, such systems are expected to reach well into the nanometer domain, and hence considerations of the mechanical behavior of materials at the nano- or atomic-scale, including those related to atomic perfection and friction, become critically important.
Carbon nanotubes, as discussed in Iijima (1991) Nature 354:56-58, have unique mechanical and electronic properties that make them outstanding candidates for nanomechanical or nanoelectromechanical applications, such as nanoscale electronics, see Collins et al. (1997) Science 278:100-103, and nanoscale mechanical systems, see Iijima (1998) Proc. IEEE Eleventh annual International Workshop on Micro Elector Mechanical Systems (IEEE, Heidelberg, Germany), 520-525. For a discussion of the mechanical properties of carbon nanotubes see Iijima et al. (1996) J. Chem. Phys. 104:2089-92, Poncharal et al. (1999) Science 283:1513-16, and Wagner, et al. (1998) Appl. Phys. Let. 72:188-90. For a review of the electronic properties of carbon nanotubes see N. Hamada et al. (1992) Phys. Res. Lett. 68:1579-81, and Saito et al. (1992) App. Phys. Let. 60:2204-6.
Multiwall carbon nanotubes (MWCNTs) comprise concentric cylindrical layers or shells of graphite-like sp2-bonded carbon, where the intershell interaction is predominantly van der Waals. In analogy to the well-known lubricating properties of van der Waals bonded graphite, the individual cylinders of MWNTs might be expected to easily slide or rotate with respect to one another, forming near-ideal linear and rotational nanobearings. Recent theoretical calculations disclosed by Kolmogorov et al. ((2000) Bulletin of the APS, March Meeting 2000, Minneapolis, Minn. (American Institute of Physics)) and Crespi et al.((1999) in Electronic Properties of Novel Materials—Science and Technology of Molecular Nanostructures, Kuzmany et al., Eds. (American Institute of Physics, College Park, Md. pp. 364-368) indicate that the MWNT interlayer corrugation energy is indeed small, favoring such motion. For a MWNT, one could envision an extension mode much like the “telescoping” of a mariner's traditional spyglass. Some evidence for inadvertent MWNT telescopic extension can be found in severe mechanical stress failure mode studies, including MWNTs embedded in a stressed polymer composite, see Wagner et al. (1998) Appl. Phys. Let. 72:188-90, and for MWNTs torn apart in quasi-static tensile stress measurements performed in a scanning electron microscope, see Yu et al. (2000) Science 287:637-640. However, no demonstration of controlled and reversible telescoping of MWNTs has been previously achieved.
A major difficulty in initiating controlled telescoping in MWNTs is the commonly capped ends that seal in all inner core nanotube cylinders. Even if the MWNT ends are opened by methods such as acid etching, it is difficult to selectively contact only the core tubes. Recently, a method has been disclosed whereby the ends of a MWNT can be carefully opened, removing the caps from just the outer shell nanotubes while leaving the core nanotubes fully intact and protruding, see Cumings et al. (2000) Nature 406:586. It has been found that the method of Cumings et al. can be used to attach a moveable nanomanipulator to the core nanotubes within a MWNT. This attachment allows for in-situ manipulation of the nanotube core thereby providing controlled reversible telescoping. Robust ultra-low friction linear nanobearings and (constant-force) nanosprings are demonstrated.